1. Field of the Invention
The invention relates to an improved method of controlling reactor temperature in the reactor of an ebullated bed process. More particularly, the invention relates to blending a residual hydrocarbon oil feedstock with an aromatic feedstock. Most particularly, the invention relates to adding the aromatic feedstock to the residual hydrocarbon oil feedstock at a rate whereby reactor temperature is maintained at a selected catalytic reaction temperature.
2. Description of Other Relevant Methods in the Field
The ebullated bed process comprises the passing of concurrently flowing streams of liquids or slurries of liquids and solids and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in random motion in the liquid and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. This technology has found commercial application in the upgrading of heavy liquid hydrocarbons and converting coal to synthetic oils.
The process is generally described in U.S. Pat. No. Re. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapor along with the liquid which is being hydrogenated pass through that upper level of catalyst particles into a substantially catalyst free zone and are removed at the upper portion of the reactor.
In an ebullated bed process the substantial amounts of hydrogen gas and light hydrocarbon vapors present rise through the reaction zone into the catalyst free zone. Liquid is both recycled to the bottom of the reactor and removed from the reactor as product from this catalyst free zone. Vapor is separated from the liquid recycle stream before being passed through the recycle conduit to the recycle pump suction. The recycle pump (ebullation pump) maintains the expansion (ebullation) and random motion of catalyst particles at a constant and stable level.
U.S. Pat. No. 3,681,231 to S. B. Alpert et al teaches an ebullated bed process wherein a petroleum residuum feedstock containing at least 25 vol % boiling above 975.degree. F. is blended with an aromatic diluent boiling within the range of 700.degree. F. to 1000.degree. F. and API gravity less than 16.degree.. The aromatic diluent is blended in a ratio of 20 to 70 vol %, preferably 20 to 40 vol % diluent based on feed.
Aromatic diluents include decant oils from fluid catalytic cracking processes, syntower bottoms from Thermofor catalytic cracking operations, heavy coker gas oils, cycle oils from cracking operations and anthracene oil obtained from the destructive distillation of coal. It is stated that the 700.degree. F. to 1000.degree. F. gas oil generated in the process will in certain cases fall within the range of gravity and characterization factor and can serve as the aromatic feed diluent.
U.S. Pat. No. 3,412,010 to S. B. Alpert et al teaches an ebullated bed process wherein a petroleum residuum containing at least 25 vol % boiling above 975.degree. F. is mixed with a recycle 680.degree. F. to 975.degree. F. fraction and passed to the ebullated reaction zone. It was found that the recycle of a 680.degree. F. to 975.degree. F. heavy gas oil resulted in a substantial lower yield of heavy gas oil in the 680.degree. F. to 975.degree. F. range and an increased yield of naphtha and furnace oil. Substantial improvement in operability was achieved as a result of reduction in asphaltenic precipitates.
U.S. Pat. No. 4,053,390 to L. C. James incorporated herein by reference teaches a start-up procedure for an ebullated bed process. In the procedure, a light oil is used to establish an ebullating bed. A heavy residual oil feedstock is incrementally substituted for the light oil. Hydrogen gas flow rate and ebullating pump speed are set to maintain ebullated bed expansion. In the incrementally changing feed stream, viscosity is controlled within .+-.10% and specific gravity controlled within .+-.5% to maintain a constant expansion of the ebullated bed, at a constant ebullating pump rate and gas flow rate.
U.S. Pat. No. 3,668,116 to C. E. Adams et al incorporated herein by reference teaches an ebullated bed process wherein the catalyst contains the oxide or sulfide of a Group VIB metal and the oxide or sulfide or a Group VIII metal deposited on a support of silica-stabilized alumina. In the drawing a resid feedstock furnace and a make-up hydrogen furnace are shown to be conventional.